Abstract

A new technique for the fast implementation of Brillouin Optical Time Domain Analysis (BOTDA)
is proposed and demonstrated, carrying the classical BOTDA method to the dynamic sensing
domain. By using a digital signal generator which enables fast switching among 100 scanning
frequencies, we demonstrate a truly distributed and dynamic measurement of a 100m long fiber
with a sampling rate of ~10kHz, limited only by the fiber length and the frequency granularity.
With 10 averages the standard deviation of the measured strain was ~5 µε.

Figures (8)

An example of F-BOTDA fast sweep assembled from three frequencies. Normally, such a sweep
comprises between 100 and 200 different frequencies. (a) A sequence of fixed frequency pump
pulses meet probe waves of different frequencies. (b) The probe frequency is fixed while the
frequency of the pump pulse changes from one pulse to the other.

The 100m FUT comprising five sections of SMF fiber. The two sections of 0.9m (a) and 1.4m
(b) are mounted on manually stretching stages, making it possible to adjust their static
Brillouin frequency shifts. Additionally, audio speakers are physically attached to these two
sections in order to induce fast strain variations of various frequencies and magnitudes.
Segment c is loosed as the rest of the fiber.

A zoom in on the last 20m of the 100m fiber, having two sections of 90cm and 140cm long
stretched to a static strain of ~800με. The interrogation of the whole 100m
fiber took 1.2ms, including 10 averages.

On the right: Top view of Fig. 4, indicating the
locations of the vibrating (a and b) and non-vibrating
(c) segments of the FUT. On the left: the measured frequency distribution of
the BGS as a function of time at three different segments of the FUT
(z=za, z=zb and z=zc). Navg=10. Vibrations of 100Hz and 80Hz are clearly observed at
segments a and b, while segment c is static.

(a) A 2D cut through the 3D M(⋅)matrix at z = zb,
describing the measured BGS of segment b 80Hz vibrations as a function of time.
The black line is an additional cut through the plotted 2D at frequency f =
f3dB = 10.93GHz, showing the Brillouin gain variations as a
function of time, at z = zb at a frequency
located at the middle of the BGS slope. Thus, if one cuts the 3D matrix at f
= f3dB, a full Distance-Time Gain picture for the whole fiber is
obtained from a single frequency probing. (b) A 2D cut from the 3D M(⋅)matrix at f = f3dB,
describing the Brillouin gain as a function of time at the frequency
f3dB along the entire FUT. f3dB
designates the frequency at the middle of the slope of the averaged BGS. This technique is
called SA-BOTDA [3].